1. Field of the Invention
The present invention relates to a fuel tank system which stores an ethanol-gasoline blended fuel obtained by blending ethanol with gasoline.
2. Description of the Related Art
Recently, it has been studied that an ethanol-gasoline blended fuel is employed as an automobile fuel. Bioethanol obtained by fermentation and distillation of plant substances, for example, agricultural crops such as sugar cane and corn can be used as the ethanol. By properly managing soil, the plant substances can provide a so-called carbon neutral effect. The carbon neutral effect means that since a plant as a feedback in itself has already absorbed carbon dioxide, the amount of carbon dioxide to be emitted is equal to the amount of carbon dioxide absorbed by the plant itself when ethanol obtained from the plant substance is burned, and total emissions of carbon dioxide theoretically become zero. Accordingly, by using the ethanol-gasoline blended fuel as an automobile fuel, the emissions of carbon dioxide can be reduced, so as to contribute to the prevention of global warming.
When considered as a fuel, the ethanol has a high octane rating, and excellent anti-knocking properties in comparison with gasoline. Therefore, by using the ethanol as a fuel, knocking that limits the performance of an internal combustion engine can be suppressed.
However, in order to use only the ethanol as a fuel, high levels of ethanol is required, and also, the ethanol has less calorific value per unit volume than gasoline. Thus, the fuel consumption rate per unit volume could be deteriorated though thermal efficiency is improved by suppressing the knocking. Furthermore, since the ethanol is derived from plants, there is a limit to the amount of production.
Meanwhile, it is known that the knocking of an internal combustion engine occurs when the internal combustion engine is heavily loaded, and is unlikely to occur when the internal combustion engine is lightly loaded. Accordingly, by using the high levels of ethanol as a fuel only at the time of high load, the knocking can be efficiently suppressed.
Based on such an idea, the ratio of gasoline and ethanol supplied to the internal combustion engine may be controlled in accordance with a required load of the internal combustion engine by separating the ethanol-gasoline blended fuel into a gasoline and an ethanol-water mixture in an automobile by mixing water with the ethanol-gasoline blended fuel. For example, there is known a compression-ignition internal combustion engine for leading an oxygen containing gas and a fuel enabling compressed self-ignition into a cylinder and for compressing the same for self-ignition, the compression-ignition internal combustion engine being controlled by varying the supply of a blended fuel, the supply of a liquid hydrocarbon such as gasoline, and the supply of an ethanol-water mixture according to a required load of the compression-ignition internal combustion engine (see Japanese Patent Laid-Open No. 2006-132368).
Also, the present applicant filed a gasoline-ethanol separating apparatus comprising first to fourth fuel tanks, a water tank and first to fourth metering pumps as an apparatus for separating the ethanol-gasoline blended fuel into a gasoline and an ethanol-water mixture by mixing water with the ethanol-gasoline blended fuel in order to control the ratio of gasoline and ethanol supplied to the internal combustion engine according to the required load of the internal combustion engine as described above (see Japanese Patent Laid-Open No. 2007-46538).
The gasoline-ethanol separating apparatus comprises the water tank for storing water, the first fuel tank for storing the ethanol-gasoline blended fuel, the second fuel tank for separating the ethanol-gasoline blended fuel into the gasoline and the ethanol-water mixture by mixing water therewith, the third fuel tank for storing the separated gasoline, and the fourth fuel tank for storing the separated ethanol-water mixture. The gasoline-ethanol separating apparatus further comprises the first to fourth metering pumps for transferring liquid among the water tank and the respective first to fourth fuel tanks. In order to respectively draw the gasoline stored in the third fuel tank and the ethanol-water mixture stored in the fourth fuel tank and supply the same to the internal combustion engine, a metering pump is further required for each of the third and fourth fuel tanks. As a result, the gasoline-ethanol separating apparatus inevitably has a large weight.
The present applicant further proposed a gasoline-ethanol separating apparatus which intends to reduce its weight by controlling a pressure inside the water tank and the respective first to fourth fuel tanks instead of providing the metering pumps to supply fuel (see Japanese Patent Laid-Open No. 2007-56707).
Since the metering pumps are not used in the gasoline-ethanol separating apparatus which intends to reduce its weight, the entire apparatus can be reduced in weight. However, the gasoline-ethanol separating apparatus which intends to reduce its weight is not changed in that the apparatus comprises the five tanks of the water tank and the respective first to fourth fuel tanks, and the entire apparatus is inevitably of large size. Also, since liquid is transferred by use of a difference in internal pressure of the respective tanks, the control is inevitably complicated.
Accordingly, there is demanded a system capable of separating the ethanol-gasoline blended fuel into a gasoline and an ethanol-water mixture by mixing water with the ethanol-gasoline blended fuel with a lightweight, compact and simple configuration in order to be mounted on an automobile.